LOS ANGELES, Ca., June 12 (TOTI) --

Robert Pattinson has had enough of being rejected by co-star Kristen Stewart and has demanded that the actress choose between him or her longtime love Michael Angarano.

"Robert is completely frustrated," a friend of his told OK! "If Kristen isn't interested in a serious relationship, she needs to tell him so he can move on."

The source said that Robert Pattinson is giving Kristen Stewart a few months to sort out her feelings. Pattinson wants the issue resolved by the time the two re-unite in Vancouver for the filming of Eclipse, the third installment of the Twilight franchise.

"He's asked her to choose between him and Michael this summer," said the source. "Robert's not willing to be strung along."

As great as Robert Pattinson seems to millions of fans worldwide, his charms have not been able to lure Stewart from Angarano, a Brooklyn boy she has dated since she was 14 years old. The two met while filming Speak in 2004 and have been together since.

"Michael was her first love, and a girl never forgets her first," said the insider. "He's a great guy and they've been together through thick and thin. On the other hand, she's met this exciting guy with a sexy British accent, idolized by women all over the world - and he's fallen for her. And since Robert started training for New Moon, he's hotter than ever, making him hard to resist."

Angarano and Stewart haven't been seen in public much lately, lending credibility to speculation that Stewart is falling for Pattinson. But there's an even simpler explanation to why he's keeping his distance.

"Michael just doesn't like Rob," said a friend of Stewart and Pattinson. "Would you want to see your girlfriend kiss another guy over and over again and have these hot scenes? He just doesn't want to be around it."

Robert Pattinson, for his part, isn't prepared to wait forever.

"Robert told Kristen he'd love a commited relationship, but that she couldn't have her cake and eat it too," said a source. "He's not prepared to share her with another man, and is hoping Kristen will choose him and give him a chance to show her what a loving and devoted boyfriend he can be."

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